setNextFocusableComponent no longer backward compatible

Name: gm110360 Date: 09/17/2001


java version "1.4.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta2-b77)
Java HotSpot(TM) Client VM (build 1.4.0-beta2-b77, mixed mode)


setNextFocusableComponent in JComponent is not backward compatible. In the 1.4
all JComponents within a setNextFocusableComponent chain must reside within the
same JFrame, more precisely all components need to have the same
getFocusCycleRootAncestor (). This makes it impossible to have (disabled)
JComponents which are part of a focus chain but have not (yet) been added to the
JFrame (they will have null as FocusCycleRootAncestor). results is a
IllegalArgumentException: "focusCycleRoot is not a focus cycle root of
aComponent" being thrown when you call focusNextComponent. I also got null
pointer Exceptions on the destroy of the applet, but this only happens on
Solaris/NS4 not under Windows/(NS6/IE6). Probably because a
FocusCycleRootAncestor is null :

java.lang.NullPointerException
at javax.swing.JComponent.deregisterNextFocusableComponent(JComponent.java:986)
at javax.swing.JComponent.removeNotify(JComponent.java:4302)
at javax.swing.JTable.removeNotify(JTable.java:480)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at java.awt.Container.removeNotify(Container.java:1881)
at javax.swing.JComponent.removeNotify(JComponent.java:4295)
at javax.swing.JRootPane.removeNotify(JRootPane.java:679)
at java.awt.Container.removeNotify(Container.java:1881)
at java.awt.Container.removeNotify(Container.java:1881)
at
sun.plugin.viewer.MNetscapePluginObject.destroyPlugin(MNetscapePluginObject.java:708)
at sun.plugin.navig.motif.Plugin.doit(Plugin.java:247)
at sun.plugin.navig.motif.Plugin.start(Plugin.java:105)


Here is a little demo to show the problem:

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Test
{
    JButton hello, world, advanced;
    JFrame f;
    JPanel p;

    public Test ()
    {
        f = new JFrame ();
        Container contentPane = f.getContentPane();

        p = new JPanel ();
        contentPane.add (p);
        hello = new JButton ("Hello");
        p.add (hello);
        world = new JButton ("World");
        p.add (world);
        advanced = new JButton ("Advanced Button");
        hello.setNextFocusableComponent (world);
        world.setNextFocusableComponent (advanced);
        advanced.setNextFocusableComponent (hello);
        advanced.setEnabled (false);

        ActionListener al = new ActionListener () {
            public void actionPerformed (ActionEvent e)
            {
                if (e.getSource () == hello)
                {
                    p.add (advanced);
                    advanced.setEnabled (true);
                    p.revalidate ();
                }
                else if (e.getSource () == advanced)
                {
                    p.remove (advanced);
                    advanced.setEnabled (false);
                    p.revalidate ();
                }

                FocusManager.getCurrentManager ().focusNextComponent
((JComponent) e.getSource ());
                System.out.println (((JButton) e.getSource ()).getText ());
            }
        };
        hello.addActionListener (al);
        world.addActionListener (al);
        advanced.addActionListener (al);

        f.setBounds (200, 200, 200, 200);
        f.setVisible (true);
    }

    public static void main (String[] args)
    {
        Test t;

        t = new Test ();
    }
}

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Clicking on "World" before "Hello" will throw a exception
(Review ID: 132041)
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